In order to study the specificity of histones our aims are (a) to characterize stage-specific variants of histones H2A and H2B, which we have detected in the sea urchin embryo, with regard to chemical structure and localization within the embryo; (b) to determine the specific locations of chromosomal proteins along the giant chromosome of Drosophila by the use of antibodies which we have prepared against a variety of chromosomal proteins isolated from Drosophila; (c) to characterize the phosphorylation sites of two H1 histones of Hela cells, with respect to intramolecular location, stage in the cell-cycle at which they are phosphorylated and dephosphorylated, and influence on the cell cycle. BIBLIOGRAPHIC REFERENCES: Differences in phosphorylation sites and levels among H1 histones during the Hela cell cycle. K. Ajiro, T. Borun and L.H. Cohen, Fed. Proc. 35: 1623 (1976) (Abstract). Visualization of drosphila histone H1, histone H2b and D1 in polytene chromosomes using immunofluorescent probes. C.R. Alfageme, G.T. Rudkin and L.H. Cohen, J. Cell Biol. 67: 6a (1975) (Abstract).